1. Field of the Invention
The present invention relates to an accumulator which is used as a pressure accumulator or a pulsation pressure damping device. The accumulator according to the present invention is used, for example, for a hydraulic piping in a vehicle such as a motor vehicle.
2. Description of the Conventional Art
There has been conventionally know an accumulator which is structured such that an internal space of an accumulator housing 2 is partitioned into a gas chamber 11 to which a high pressure gas is sealed and a liquid chamber 12 which is communicated with a port hole 5, by arranging a bellows 9 and a bellows cap 10 in an inner portion of the accumulator housing 2 having the port hole 5 connected to a pressure piping of a device, as shown in FIG. 12. In the accumulator, in the case that the operation of the device stops and the pressure within the pressure piping is lowered, the liquid (the oil) within the liquid chamber 12 is discharged little by little from the port hole 5, the bellows 9 is accordingly elongated little by little due to the charged gas pressure, and the bellows cap 10 comes into contact with a seal portion 15 so as to form a so-called zero-down state. The seal portion 15 is constructed by a lip seal which is provided in an inner opening peripheral edge portion of the port hole 5. Further, in this zero-down state, the liquid chamber 12 is occluded on the basis of the contact of the bellows cap 10 with the seal portion 15, the liquid is partially confined in the liquid chamber 12, and the pressure of the confined liquid is balanced with the gas pressure of the gas chamber 11. As a result, any excessive stress is not applied to the bellows 9, and it is accordingly possible to inhibit plastic deformation from being generated in the bellows 9 (refer to FIG. 6 of Japanese Unexamined Patent Publication No. 2009-092145).
However, in the case that the zero-down state due to the operation stop of the device is generated under a low temperature condition, and the temperature rises thereafter, each of the liquid and the charged gas confined in the liquid chamber 12 is thermally inflated, and the pressure rises. In this case, a rising degree of the pressure is greater in the liquid in comparison with the charged gas, however, since a pressure receiving area in the bellows cap 10 is set to be smaller than that in the charged gas side, the bellows cap 10 does not move until the liquid pressure becomes significantly greater than the gas pressure, and the bellows cap 10 does move away from the seal portion 15.
Therefore, a pressure difference stretching for about several MPa may be generated between the liquid pressure and the gas pressure in inner and outer sides of the bellows 9, and there is a risk that the plastic deformation is generated in the bellows 9 if the great pressure difference is generated as mentioned above.
In order to dissolve the disadvantage mentioned above, the inventors of the present invention have proposed previously an accumulator which is provided with the following countermeasures.
More specifically, as shown in FIG. 13, in the accumulator, a seal member 31 is retained to the port hole 5 side of the bellows cap 10 via a seal holder 21, and the seal member 31 comes into contact with the seal portion 15 at the zero-down time. The seal member 31 is constructed by a discoid rigid plate, and an outer diameter thereof is set to be larger than an inner diameter of a flange portion 21b of the seal holder 21. Therefore, the seal member 31 is retained by the seal holder 21. Further, since a thickness of the seal member 31 is set to be smaller than a distance between the flange portion 21b and the bellows cap 10, the seal member 31 can relatively move in relation to the seal holder 21 and the bellows cap 10 within a range of a dimensional difference. Further, since a spring member 41 pressing the seal member 31 is embedded between the flange portion 21b and the seal member 31, the seal member 31 is pressed to the bellows cap 10 in an initial state.
The accumulator is connected to a pressure piping of the device and is activated as follows.
Steady Activating Time
Since the seal member 31 is away from the seal portion 15 by moving together with the bellows cap 10 in a state in which the seal member 31 is retained by the seal holder 21 at the steady activating time of the accumulator as shown in FIG. 13, the port hole 5 which is open to an inner peripheral side of the seal portion 15 is open. Therefore, the port hole 5 is communicated with the liquid chamber 12. Accordingly, since the liquid having a pressure at any given time is introduced to the liquid chamber 12 from the port hole 5, the bellows cap 10 moves at pleasure together with the seal member 31 in such a manner that the liquid pressure and the charged gas pressure are balanced with each other.
Zero-Down Time
In the case that the operation of the device stops and the pressure within the pressure piping is lowered, the liquid within the liquid chamber 12 is discharged little by little from the port hole 5, and the bellows cap 10 is accordingly moved on the basis of the charged gas pressure in such a direction that the bellows cap 10 comes close to the seal portion 15. As a result, the seal member 31 comes into contact with the seal portion 15 as shown in FIG. 14 so as to form the zero-down state. Therefore, since the liquid chamber 12 is occluded and the partial liquid is confined in the liquid chamber 12, any further pressure reduction is not generated in the liquid chamber. Therefore, there is achieved a state in which the liquid pressure and the charged gas pressure are balanced in the inner and outer sides of the bellows 9.
Thermal Expanding Time in Zero-Down State
In the case that the liquid and the charged gas confined in the liquid chamber 12 are thermally expanded due to the rise of the atmosphere temperature in the zero-down state, that is, the state in which the seal member 31 comes into contact with the seal portion 15 and the liquid chamber 12 is occluded, the pressure difference is generated since the rising degree of the pressure is greater in the liquid than in the gas. However, in the accumulator, the bellows cap 10 moves toward a direction that the bellows cap 10 moves away from the seal portion 15 while compressing the spring member 41, on the basis of the pressure difference, as shown in FIG. 15. Accordingly, since the state in which the liquid pressure and the charged gas pressure are balanced is maintained, the pressure difference is not generated in the inner and outer sides of the bellows 9. As a result, it is possible to inhibit the plastic deformation from being generated in the bellows 9. At this time, since the pressure receiving area of the seal member 31 in the state in which the seal member 31 is in contact with the seal portion 15 is greater in the surface close to the bellows cap 10 side than the surface close to the seal portion 15 side, the seal member 31 does not move while being in contact with the seal portion 15 on the basis of the difference of the pressure receiving area in both the surfaces. Therefore, the port hole 5 open to the inner peripheral side of the seal portion 15 is kept closed.
As described above, according to the accumulator in FIG. 13, it is possible to reduce the pressure difference generated by the difference of coefficient of thermal expansion in the case that the liquid and the charged gas confined in the liquid chamber 12 thermally expands at the zero-down time. As a result, it is possible to inhibit the plastic deformation from being generated in the bellows 9 (refer to FIGS. 1 to 3 of Japanese Unexamined Patent Publication No. 2009-092145).
However, there has been room for improvement in the following points, in the accumulator shown in FIG. 13.
More specifically, since the accumulator shown in FIG. 13 mentioned above reduces the pressure difference which is generated by the difference of coefficient of thermal expansion in the case that the liquid and the charged gas confined in the liquid chamber 12 thermally expands at the zero-down time, there occurs such an activation that the seal member 31 does not move while being in contact with the seal portion 15 and only the bellows cap 10 moves in the direction that the bellows cap 10 moves away from the seal portion 15. Therefore, the seal member 31 is structured such as to relatively move in relation to the seal holder 21 and the bellows cap 10, and an allowance dimension for relatively moving the seal member 31 is set in the seal holder 21 for enabling the relative movement. In other words, a distance between the flange portion 21b of the seal holder 21 and the bellows cap 10 is set to be greater than a thickness of the seal member 31, and the spring member 41 is embedded between the flange portion 21b and the seal member 31 under the condition.
Therefore, according to the accumulator in FIG. 13 mentioned above, since it is necessary to embed the spring member 41 together with the seal member 31 within the seal holder 21 while setting a length of the seal holder 21 to be larger than the thickness of the seal member 31, the parts are large scaled and the number of the parts is large. On the contrary, the pressure difference reducing mechanism can be made further useful by making the parts compact and reducing the number of the parts.